Technical Field
The present disclosure relates to a packaged sensor assembly.
Description of the Related Art
As is known, attention to the development and integration of microelectromechanical environmental sensors is progressively increasing as the use of portable electronic devices, such as smartphones and tablets or other so-called “wearable” electronic devices, increases. In particular, there is noted a specific interest to enclose a microelectromechanical pressure sensor and a microelectromechanical humidity sensor within a single packaging structure for electronic devices, together with a control circuit such as an application-specific integrated circuit (ASIC). The control circuit may serve for controlling operation of the sensors and as an interface for converting the electrical signals supplied by the sensors into data that may be used by further processing stages for performing various functions.
A microelectromechanical pressure sensor generally comprises a flexible membrane, suspended over a cavity in a semiconductor substrate. The membrane is deformed by the pressure difference between the two sides. Sensitive elements, in general of a piezoelectric type, are coupled to the faces of the membrane and enable detection of the degree of deformation.
Microelectromechanical humidity sensors are, instead, usually of a capacitive type and comprise electrodes coupled together to form a capacitor and separated by a hygroscopic polymer, the dielectric constant of which varies as a function of the humidity absorbed.
A problem generally to be tackled in the integration process is determined by the contrasting application preferences of pressure sensors on the one hand and humidity sensors on the other. Both types of sensors, in fact, have to be exposed to external environmental conditions through openings in the packaging structure to be in condition of operating correctly. However, for humidity sensors it is important to maximize exposure to the external environment to favor absorption of humidity by the hygroscopic polymer, while pressure sensors prefer protection from electromagnetic radiation in the spectrum of the visible and of the infrared. In fact, incident radiation causes parasitic currents and consequent voltage drops that may alter the useful signals. Exposure to the external environment is therefore preferred to be sufficient to provide suitable fluidic connection therewith and, at the same time, should minimize the intensity of incident radiation on the membrane and, in particular, on the piezoresistive elements.
In addition to the desire to balance the contrasting preferences for pressure sensors and humidity sensors, it is also desirable to satisfy the general tendency to reduce the dimensions of devices and of the packaging structure as a whole, to render use of electronic devices more flexible and convenient.